drm/amdgpu: Call amdgpu_device_unmap_mmio() if device is unplugged to prevent crash in GPU initialization failure

[Why]
In amdgpu_driver_load_kms, when amdgpu_device_init returns error during driver modprobe, it
will start the error handle path immediately and call into amdgpu_device_unmap_mmio as well
to release mapped VRAM. However, in the following release callback, driver stills visits the
unmapped memory like vcn.inst[i].fw_shared_cpu_addr in vcn_v3_0_sw_fini. So a kernel crash occurs.

[How]
call amdgpu_device_unmap_mmio() if device is unplugged to prevent invalid memory address in
vcn_v3_0_sw_fini() when GPU initialization failure.
Signed-off-by: Leslie Shi <Yuliang.Shi@amd.com>
Reviewed-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>